Surface potential measuring system

ABSTRACT

In a system for measuring a surface potential of a sample, a probe is located above. A surface of the sample with a small gap and is vibrated by a piezoelectronic element which is energized by a oscillator. A potential of the distal end of the probe is changed and is converted into an electrical signal. The surface potential is obtained from the electrical signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vibration type probe structure formeasuring the surface potential of a surface of a sample in a noncontactmanner and a surface potential measuring system using the same.

2. Description of the Related Art

As a conventional system for measuring charges on a surface of a sample,a noncontact type surface potential measuring system shown in FIG. 1 isknown. In the system shown in FIG. 1, a measurement hole 100a is formedin the bottom of a shield case 100, and a flat sample 102 having asurface potential E is placed under the measurement hole 100a. A flatprobe electrode 101 is arranged in the shield case 100 so as to opposethe sample 102 at a predetermined distance. A sector 103 as a shutter isarranged between the measurement hole 100a and the probe electrode 101.The sector 103 is connected to a solenoid 104 for driving the sector103, a solenoid driver 105 for energizing the solenoid 104, and anoscillator 106 for generating an oscillation signal. A signal generatedby the oscillator 106 is amplified by the solenoid driver 105 and issupplied to the solenoid 104. The solenoid 104 then drives the sector103. The sector 103 is moved parallel to the measurement hole 100a toopen and close it. In addition, an amplifier 107 and a synchronousdetection circuit 108 are connected to the probe electrode 101 throughresistors R1 and R2 and a capacitor C.

In this conventional surface potential measuring system, some of linesof electric force extending from the surface of the sample 102 reach asurface of the probe electrode 101 through the measurement hole 100a,and their amount φ is changed at a constant period upon anopening/closing operation of the sector 103. Therefore, a currentproportional to dφ/dt flows through the load of the probe electrode 101,and an AC voltage e having a predetermined period is generated acrossthe two ends of the capacitor R1 upon the opening/closing operation ofthe sector 103. The AC voltage e is proportional to the surfacepotential E of the sample 102 provided that the amplitude and frequencyof the sector 103 and the distance from the probe electrode 101 to thesample 102 are constant.

The AC voltage e detected by the probe electrode 101 has a much smallerlevel than the surface potential E of the sample 102. For this reason,the AC voltage e is amplified by the amplifier 107 to a predeterminedlevel and is converted into a DC voltage by the synchronous detectioncircuit 108 in synchronism with the oscillation frequency of theoscillator 106, i.e., the opening/closing operation of the sector 103 soas to be output as a measurement signal.

In this conventional surface potential measuring system, in order toobtain a measurement output proportional to the surface potential E ofthe sample 102, a signal to be detected by the probe electrode 101 mustbe a signal which is not much influenced by external noise and has apredetermined level or more.

For this purpose, the surface area of the probe electrode 101 must beincreased, and the measurement hole 100a must be formed to have apredetermined size or more (generally, 3 mm square or more). In theconventional surface potential measuring system, therefore, the surfacepotential E of the sample 102 cannot be measured unless the sample 102has an area of about 10 mm² or more. That is, a surface potential in asmall area smaller than an area of 10 mm² cannot be measured. Inaddition, since the selector 103 as a shutter is arranged between theprobe electrode 101 and the sample 102, the distance between the probeelectrode 101 and the sample 102 is undesirably increased, resulting inpoor detection sensitivity.

Furthermore, in the conventional noncontact type surface potentialmeasuring system, a detection current value error is caused uponmeasurement due to temperature drift and the like. For example, the biascurrent of a detection amplifier is changed with a change intemperature, whereas the permittivity of a capacitance determined by thesample and the probe structure is changed with a change in humidity.Therefore, such an error must be corrected.

For this purpose, in the conventional system, prior to measurement, areference voltage is applied to a conductive plate arranged in place ofthe sample 102. The reference voltage is changed, and a value measuredby the surface potential measuring system at this time is calibrated.Thereafter, the sample 102 is placed under the system so as to measureits surface potential.

In such a method, however, a measurement value under the conditions ofcalibration is changed over time due to drift such as temperature drift.In order to perform high-precision measurement, therefore, measurementmust be quickly started and completed after calibration so as to preventthe influences of temperature drift and the like. However, if, forexample, a transfer drum used for a copying machine or a transfer diskused for a system for measuring the surface potential of a disk is asample, since it has a large measurement area, a long measurement timeis required. As a result, a measurement error caused by temperaturedrift and the like cannot be neglected, and stable, high-precisionmeasurement cannot be performed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a vibration typeprobe which has good detection sensitivity and can measure a surfacepotential within a small area with high precision, and a surfacepotential measuring system using the same.

It is another object of the present invention to provide a surfacepotential measurement sample from which a stable, high-precisionmeasurement value can be obtained, and a system for correcting themeasurement value.

According to the present invention, there is provided a system formeasuring a surface potential of a sample, comprising:

probe means, having a distal end located near a measurement surface witha gap, for probing the surface potential;

vibrating means for vibrating the probe means to change the gap betweenthe distal end and the measurement surface; and

detecting means for detecting a change in potential of the distal end ofthe probe means and converting the change into a measurement signalcorresponding to the surface potential of the sample.

In addition, according to the present invention, there is provided asystem for measuring a surface potential of a sample having a surfaceregion, comprising:

probe means, having a distal end located near a measurement surface witha gap, for probing the surface potential of the measurement surface;

vibrating means for vibrating the probe means to change the gap betweena distal end of the probe means and the measurement surface;

holding means for holding the probe means, which is vibrated by thevibrating means, so as to allow the probe means to be vibrated;

means for maintaining a substantially constant gap between the holdingmeans and a region retrieved by the probe means; and

detecting means for detecting a change in potential of the vibrateddistal end of the probe means and converting the change into ameasurement signal corresponding to a surface potential of the sample.

In addition, according to the present invention, there is provided asample whose surface potential is to be measured, comprising:

a surface whose surface potential is to be measured; and

means, arranged on the surface, for receiving a reference potential.

Furthermore, according to the present invention, there is provided asystem for reading a radiation image, comprising:

an image plate obtained by stacking a phosphor layer sensitive toradiation and emitting light and a photosensitive layer sensitive to thelight emitted from the phosphor layer on a substrate, a latent imagecorresponding to a radiation transmission image being formed on theimage plate;

means for urging a dielectric recording sheet against the photosensitivelayer of the image plate so as to transfer the latent image formed onthe photosensitive layer onto the dielectric recording sheet; and

means for reading the latent image by measuring a potential of thelatent image transferred onto the dielectric recording sheet andconverting the potential into an electrical signal.

Moreover, according to the present invention, there is provided a systemfor reading a radiation image, comprising:

an image plate obtained by stacking a phosphor layer sensitive toradiation and emitting light and a photosensitive layer sensitive to thelight emitted from the phosphor layer on a substrate;

a charger for uniformly charging the photosensitive layer of the imageplate;

a dielectric recording sheet for transferring a latent image which isformed on the photosensitive layer in accordance with a radiationtransmission image formed on the image plate;

a transfer roller for urging the dielectric recording sheet against thephotosensitive layer of the image plate on which the latent image isformed; and

means for reading the latent image by measuring a potential of thelatent image transferred onto the dielectric recording sheet andconverting the potential into an electrical signal.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a block diagram showing a conventional system for measuringthe potential of a surface of a sample to be measured;

FIG. 2 is a block diagram showing a system for measuring the surfacepotential of a sample, which incorporates a vibration type probestructure according to an embodiment of the present invention;

FIG. 3 is a view for explaining a principle of measurement by means ofthe vibration type probe structure in FIG. 2;

FIG. 4 is a sectional view showing a vibration type probe structureaccording to another embodiment of the present invention;

FIG. 5 is a block diagram showing a system for measuring the surfacepotential of a sample, which incorporates the vibration type probestructure in FIG. 4;

FIG. 6 is a perspective view showing a sample whose surface potential ismeasured by the surface potential measuring system in FIG. 5;

FIGS. 7A, 7B, and 7C are perspective views respectively showing othersamples whose surface potentials are measured by the surface potentialsystem in FIG. 5;

FIG. 8 is a view for explaining a principle of measuring a gap lengthbetween the probe electrode and a surface of the sample in FIG. 4;

FIG. 9 is a plan view showing the sample on which a measurementexperiment of a surface potential is performed by the system in FIG. 4;

FIG. 10 is a sectional view of the sample in FIG. 9;

FIGS. 11 and 12 are graphs showing measurement results of measurementexperiments;

FIGS. 13A, 13B, and 13C graphs showing other experiment results obtainedfrom measurement experiments performed by the system in FIG. 4;

FIG. 14 is a perspective view showing a schematic arrangement of anX-ray imaging apparatus for transferring a latent image onto an imageplate whose surface potential is measured by the measuring system of thepresent invention;

FIG. 15 is a sectional view showing an image plate in FIG. 14;

FIGS. 16A to 16E are views for explaining an imaging operation of theX-ray imaging apparatus shown in FIG. 14;

FIG. 17 is a block diagram showing a system for measuring anelectrostatic potential for reading a recording sheet on which a latentimage is transferred according to still another embodiment of thepresent invention; and

FIG. 18 is a perspective view showing a schematic arrangement of anapparatus constituting a rotating recording disk from which data can beread by the system in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows a vibration type probe structure according to the presentinvention and a system for measuring a surface potential distribution ofa sample to be measured by using the same. As shown in FIG. 2, thevibration type probe structure is constituted by a needle-like probeelectrode 1 and a piezoelectric element 2 coupled to the upper portionof the probe electrode 1. The probe electrode 1 is arranged in a shieldcase 3 having a measurement hole 3a formed in its bottom in such amanner that the distal end of the probe electrode 1 opposes a flatsample 4 having a surface potential E, which is located under themeasurement hole 3a, at a predetermined distance. A piezoelectric driver5 and an oscillator 6 are connected to the piezoelectric element 2 forvibrating the probe electrode 1 in a direction perpendicular to ameasurement surface of the sample 4 as indicated by arrows in FIG. 2. Asignal generated by the oscillator 6 is amplified by the piezoelectricelement driver 5 and is supplied to the piezoelectric element 2. Thepiezoelectric element 2 is then driven. As a result, the probe electrode1 is vertically vibrated. A synchronous detection circuit 8 and anintegrator 9 consisting of a resistor R5 and a capacitor C1 areconnected to the probe electrode 1 through resistors R3 and R4 and anamplifier 7. The position of the sample 4 is fixed. A measurementsurface 4a (to be subjected to measurement) facing the probe electrode 1is formed on the sample 4 so as to be flat with a sufficient surfaceprecision.

In the surface potential measuring system including the vibration typeprobe structure according to the present invention, when the oscillator6 is oscillated to generate an oscillation signal, and the oscillationsignal is amplified by the piezoelectric element driver 5 so as tovertically vibrate the piezoelectric element 2, the probe electrode 1coupled to the piezoelectric element 2 is also vertically vibrated atthe oscillation frequency of the oscillator 6. When the probe electrode1 is vertically vibrated at a predetermined period, since the distancefrom the measurement surface 4a of the sample 4 located under the probeelectrode 1 to the probe electrode 1 is periodically changed, some oflines of electric force which are generated from the measurement surface4a in accordance with the period reach the probe electrode 1. Therefore,as described above, a signal detected by the probe electrode 1 isgenerated as an AC signal which has the vibration period of thepiezoelectric element 2 and is proportional to a surface potential E ofthe measurement surface 4a. The AC signal is amplified by the amplifier7 and is subjected to synchronous detection in the synchronous detectioncircuit 8 at the same period as the vibration period of the probeelectrode 1. The signal is then averaged by the integrator 9 and isoutput as a measurement value corresponding to the surface potential Eof the measurement surface 4a.

A principle of measuring the surface potential of a sample by using thevibration type probe structure shown in FIG. 2 will be described withreference to FIG. 3. Assume, as shown in FIG. 3, that the surface areaof the distal end of the probe electrode 1 is represented by S, thedistance between a vibrating center which is defined as an intermediatepoint of a vibration range of the distal end of the probe electrode 1and the sample 4 is represented by d, and a specific permittivity isrepresented by s. In this case, if only the distal end of the probeelectrode 1 is influenced by lines of electric force from the sample 4,a capacitance C1 between the distal end of the prove electrode 1 and thesample 4 is represented by:

    C1.sub.1 =εs·S/d                          (1)

If the equivalent input capacitance of a detector system 7 constitutedby an amplifier and the like which is connected to the probe electrode 1is represented by C0, the surface potential E of the sample 4 is dividedby capacitors C1 and C0. Therefore, a voltage across the two ends of thecapacitor C0, i.e., a detection voltage Ed detected by the probeelectrode 1 is represented by

    Ed=C1·E/(C1+C0)                                   (2)

In this case, if the probe electrode 1 is vibrated by the vibratingelement 2 such as a piezoelectric element at an arbitrary predeterminedperiod in a direction perpendicular to the sample 4, since the distanced between the probe electrode 1 and the sample 4 is periodicallychanged, the value of C1 given by equation (1) is changed accordingly.With the change in C1, the detection voltage Ed detected by the probeelectrode 1 is output as an AC signal obtained by modulating the surfacepotential E of the sample 4 with the vibrations of the probe electrode 1according to equation (2).

According to equations (1) and (2), detection sensitivity for thedetection voltage Ed detected by the probe electrode 1 can be improvedby increasing the value of C1. For this purpose, the probe electrode 1is located nearer to the sample 4 to decrease the distance d between theprobe electrode 1 and the sample 4. In order to obtain a high-precision,stable measurement result, the distance d between a vibrating center ofthe probe electrode 1 and the sample 4 is preferably held in a constant.

With such a vibration type probe structure in which the distal end ofthe probe electrode 1 is located near and opposite the measurementsurface 4a, stable, high-precision measurement of a surface potentialcan be performed with respect to the sample 4 whose position is fixedand which has the measurement surface 4a formed to be flat withsufficient surface precision.

Since the distal end of the probe electrode 1 is located near themeasurement surface 4a, the detection sensitivity is improved, and thedetection resolution can be increased. This allows high-precisionmeasurement in a small area.

FIG. 4 shows a vibration type probe structure according to anotherembodiment of the present invention. As shown in FIG. 4, a needle-likeprobe electrode 11 is inserted in a cylindrical housing 10 having ahinge portion 10a formed around its outer surface such that the distalend of the probe electrode 11 protrudes from the housing 10. The probeelectrode 11 is fixed by an insulating material 12 such as Teflon filledin the housing 10. The distal end of the probe electrode 11 is locatednear and opposite a sample 13. A cylindrical piezoelectric element 14 isarranged around the outer surface of the housing 10. The lower portionof the piezoelectric element 14 is fixed to the hinge portion 10a of thehousing 10. The upper portion of the piezoelectric element 14 is fixedto the lower portion of a case 16 in which an amplifier 15 connected tothe probe electrode 11 is housed. Mirror cases 17 and 18 are arrangedoutside the piezoelectric element 14 and the case 16 so as to besymmetrical about the probe electrode 11. A light source 19 such as alaser diode (LD) for emitting a light beam and a PSD (semiconductorposition detecting element) 20 as a position sensor for detecting theposition of a light beam are respectively arranged in the upper portionsof the mirror cases 17 and 18. Mirrors 21 and 22 are respectivelyarranged in the lower portions of the mirror cases 17 and 18. The mirror21 is positioned to cause a laser beam a1 emitted from the light source19 to be incident on a measurement surface 13a of the sample 13 locatedright under the distal end of the probe electrode 11. The mirror 22 ispositioned to guide a laser beam a2 reflected by the measurement surface13a to the PSD 20. The mirrors 21 and 22 are located near the sample 13so as to increase the incident angle of the laser beam which is incidenton the measurement surface 13a located right under the probe electrode11 and to increase the reflection angle of the laser beam. Lens systems(not shown) for transmitting laser beams are respectively arrangedbetween the light source 19 and the mirror 21 in the mirror case 17 andbetween the PSD 20 and the mirror 21 in the mirror case 18. Anoscillator and a piezoelectric driver are connected to the piezoelectricelement 14.

In the vibration type probe structure shown in FIG. 4, the oscillator isoscillated to generate an oscillation signal, and the oscillation signalis amplified by the piezoelectric driver so as to vertically vibrate thepiezoelectric element 14. With this operation, the housing 10 having thehinge portion 10a to which the lower portion of the piezoelectricelement 14 is fixed, and the probe electrode 11 fixed in the housing 10with the insulating material 12 are vertically vibrated at theoscillation frequency of the oscillator. When the probe electrode 11 isvertically vibrated at a predetermined period, since the distancebetween the probe electrode 11 and the measurement surface 13a of thesample 13 located thereunder is periodically changed, some of lines ofelectric force generated from the measurement surface 13a reach theprobe electrode 11 in accordance with the period. A signal detected bythe probe electrode 11 is generated as an AC signal which has theoscillation period of the piezoelectric element 14 and is proportionalto the surface potential of the measurement surface 13a. The AC signalis amplified by the amplifier 15, and is output as a measurement signalcorresponding to the surface potential of the measurement surface 13athrough a detector system constituted by a synchronous detectioncircuit, an integrator, and the like.

In this measurement process, the laser beam a1 emitted from the lightsource 19 is reflected by the mirror 21 so as to be incident on themeasurement surface 13a of the sample 13 located right under the distalend of the probe electrode 11. The reflected laser beam a2 is thenguided to the PSD 20 through the mirror 22. If the sample 13 isdisplaced vertically, i.e., in the height direction, the reflected laserbeam a2 is deflected in accordance with the displacement amount, and theincident position of the beam on the PSD 20 is horizontally moved. Byextracting an electrical signal proportional to this movement amountfrom the PSD 20, the vertical displacement amount of the measurementsurface 13a with respect to a reference surface, i.e., the bottomsurfaces of the mirror cases 17 and 18 can be measured. Therefore, evenif the sample 13 is vertically displaced, the distance between thedistal end of the probe electrode 11 and the sample 13 can be accuratelymeasured. Consequently, even if the sample 13 has poor surface precisionor the sample 13 is rotated or moved, an accurate measurement value canbe obtained by correcting a detection voltage (AC signal) detected bythe probe electrode 11 in accordance with the displacement amount of thesample

Since the piezoelectric element 14 for vibrating the probe electrode 11is formed to have a cylindrical shape and is fixed to the hinge portion10a of the housing 10 in which the probe electrode 11 is fixed with theinsulating material 12, a space is formed above the probe electrode 11.With this arrangement, the amplifier 15 for amplifying a detectionvoltage (AC signal) detected by the probe electrode 11 can be locatednear and connected to the upper portion of the probe electrode 11.Therefore, the influences of external noise and the like on a detectionsignal detected by the probe electrode 11 can be reduced, and ahigh-precision measurement value can be obtained.

In addition, since the distal end of the probe electrode 11 can belocated near the sample 13, excellent detection sensitivity can berealized, and the measurement resolution can be increased, thus allowinghigh-precision measurement of a surface potential within a small area.

FIG. 5 shows a system, having the vibration type probe structure shownin FIG. 4, for measuring the potential distribution of a surface of asample. As shown in FIG. 5, a spindle 32, a driving motor 33, and a gapcontrol unit 35 are arranged on an antivibration base 30. The spindle 32serves to rotate a disk-like sample 31. A vibration type probe structure34 for measuring the surface potential of a measurement surface 31a ofthe sample 31 is mounted on the gap control unit 35. In addition, thissystem includes a surface potential detector 36 for receiving a signaldetected by the vibration type probe 34 and outputting a measurementvalue corresponding to the surface potential of the measurement surface31a, and a measurement value correcting unit 60 for correcting themeasurement value.

As shown in FIG. 6, a correcting electrode 70 is formed at a peripheralportion on the measurement surface 31a of the sample 31. The correctingelectrode 70 is formed by depositing a chromium pattern having athickness of several hundreds Å and a width of several mm (outermostperiphery). A reference voltage is applied from a reference power source61 to the correcting electrode 70 through a rotary connector 65. Thiscorrecting electrode 70 may be formed on a table for supporting a sampleinstead of forming it on the sample 31.

The detector 36 arranged above the vibration type probe structure 34comprises a piezoelectric element driver 37, an oscillator 38, asynchronous detection circuit 39, an integrator 40 consisting of aresistor R6 and a capacitor C2, and the above-mentioned amplifier 15. Asignal generated by the oscillator 38 is amplified by the piezoelectricelement driver 37 so as to drive the piezoelectric element 14. As aresult, the probe electrode 11 is vertically vibrated.

The gap control unit 35 comprises: a table 41 movably mounted on theantivibration base 30; a main body 42 fixed to the table 41; an arm 43substantially parallel to the sample 31 and integrally coupled to themain body 42, through an elastic hinge portion 42a; a gap controlcoupling spring 46 for coupling a gap control piezoelectric element 45,which is coupled between a protruding portion 42b formed on the upperportion of the main body 42 and the arm 43 through a gap adjusting screw44, between a protruding portion 42c formed on the lower portion of themain body 42 and the arm 43; a gap detector 47 connected between thevibration type probe 34 and the piezoelectric element 45; and a gapcontrol circuit 48.

The vibration type probe structure 34 is attached to a support member 49fixed to the distal end of the arm 43. The distal end of the probeelectrode 11 is located near the measurement surface 31a of the sample31 (with a gap of about several tens μm) so as to oppose the measurementsurface 31a and to be movable along its radial direction. A gap betweenan unvibrated end of the structure 34 and the measurement surface 31a iscontrolled by the gap control unit. That is, the gap between thevibrating center of the distal end of the probe electrode 11 and themeasurement surface 31a is controlled by the gap control unit 35.

The gap control circuit 48 comprises a differential amplifier 50 and avariable voltage power source 51 for generating a gap setting voltage,i.e., a reference voltage. The piezoelectric element 45 is arranged onthe side of the elastic hinge portion 42a at a position where the arm 43is divided at a ratio of, e.g., 1 to 10. In addition, a driving motor 53is coupled to the table 41 through a feed screw bar 52. When the feedscrew bar 52 is rotated by the driving motor 53, the table 41 islaterally moved. Upon this movement, the probe electrode 11 of thevibration type probe structure 34 attached to the distal end of the arm43 is moved along the radial direction of the measurement surface 31a ofthe sample 31.

An operation of the system which has the above-described arrangement andserves to measure a surface potential distribution will be describedbelow.

The sample 31 mounted on the spindle 32 is rotated by the driving motor33 at a predetermined speed. The probe electrode 11 is moved from theouter periphery of the measurement surface 31a toward its center (mayalso be moved in the opposite direction) upon driving of the drivingmotor 53. In the above-described manner, the surface potential of themeasurement surface 31a is measured. More specifically, an oscillationsignal from the oscillator 38 is amplified by the piezoelectric elementdriver 37 so as to vertically vibrate the cylindrical piezoelectricelement 14. Since the piezoelectric element 14 is fixed to the hingeportion 10a of the housing 10, the housing 10 is vibrated integrallywith the piezoelectric element 14. Upon this vibration, the probeelectrode 11 fixed in the housing 10 with the insulating material 12 isalso vertically vibrated at the oscillation frequency of the oscillator38. When the probe electrode 11 is vertically vibrated at apredetermined period, since the distance (gap) between the probeelectrode 11 and the measurement surface 31a of the sample 31 locatedthereunder is periodically changed, some of lines of electric forceextending from the measurement surface 31a reach the probe electrode 11in accordance with the period. Therefore, a signal detected by the probeelectrode 11 is obtained as an AC signal which has the same vibrationperiod as that of the piezoelectric element 14 and is proportional tothe surface potential of the measurement surface 31a. This AC signal isamplified by the amplifier 17. The amplified signal is then subjected tosynchronous detection at the same period as the oscillation period ofthe oscillator 38 and is averaged by the integrator 40. As a result, thesignal is output as a measurement value corresponding to the surfacepotential of the measurement surface 31a.

In this manner, the surface potential of the measurement surface 31a ofthe sample 31 is measured. Although the measurement value includes anerror due to drift such as temperature drift, the error is corrected bythe measurement value correcting unit 60. More specifically, a referencevoltage is applied to the correcting electrode 70, which is formed on aportion of the measurement surface 31a or of the table for supportingthe sample in advance, through the rotary connector 65. The surfacepotential of the correcting electrode 70 is then measured by themeasuring system in the same manner as described above. The detectionvoltage corresponding to the surface potential of the correctingelectrode 70, i.e., a detection signal E1 is stored in a memory storageunit 63. Thereafter, the sample 31 is rotated, and the surface potentialof the measurement surface 31a is measured as described above, and isstored in the memory unit 63. The sample 31 is rotated to measure thesurface potential of the correcting electrode 70 again. A detectionvoltage E2 measured at this time is stored in the storage unit 63.

The detection signals E1 and E2 stored in the memory unit 63 are inputto an arithmetic unit 62 so as to calculate the difference between thedetection voltages E1 and E2 as a drift voltage E3 (=the detectionvoltage E1-the detection voltage E2). The drift voltage E3 is subtractedfrom the measurement data of the surface potential of the measurementsurface 31a stored in the memory unit 63, and a measurement value upondrift correction is displayed on a display unit 64.

Similar to the above-described operation, the probe electrode 11 ismoved from the outer periphery of the measurement surface 31a toward itscenter (or in the opposite direction), and the surface potential of thecorrecting electrode 70 is measured at a position, which is assumedafter the sample 31 is rotated once or a predetermined number of timesas in the above-described manner, before and after measurement of thesurface potential of the measurement surface 31a, and the differencebetween the measured surface potentials, i.e., a drift voltage isobtained. The measurement value, i.e., the surface potential of themeasurement surface 31a is then corrected by subtracting the driftvoltage from the measurement data based on the surface potential of themeasurement surface 31a.

According to another embodiment, a reference voltage (E11, E12, E13 . .. E1N) applied from the reference power source 61 to the correctingelectrode 70 through the rotary connector 65 is linearly changed everytime the probe electrode 11 is located right under the correctingelectrode 70 formed on the measurement surface 31a while the probeelectrode 11 is moved from the outer periphery of the measurementsurface 31a of the rotating sample 31 toward its center (or in theopposite direction), and the applied voltage (E11, E12, E13 . . . E1N)at each time is stored. Detection voltages (E21, E22, E23 . . . E2N)which are output from the surface potential detector 36 of a surfacepotential measuring system at the respective timings are stored in thememory unit 63. The applied voltages (E11, E12, E13 . . . E1N) and thedetection voltages (E21, E22, E23 . . . E2N) stored in the storage unit63 are input to the arithmetic unit 62. The applied voltages (E11, E12,E13 . . . E1N) are then respectively compared with the detectionvoltages (E21, E22, E23 . . . E2N) so as to calculate linearity of thegain of the surface potential measuring system. The surface potentialmeasurement data of the measurement surface 31a is corrected on thebasis of this calculation result and is displayed on the display unit64.

In the above-described embodiments, the measurement value of the surfacepotential of the measurement surface 31a which is subjected to driftcorrection is displayed on the display unit 64. However, the measurementvalue may be stored in the storage unit 63 so as to be read out asneeded.

Furthermore, in the above-described embodiments, the correctingelectrode 70 is formed on a portion of the disk-like sample 31. However,measurement values can be corrected in the same manner as describedabove by forming correcting electrodes 70A, 70B, and 70C on portions ofdrum-like, card-like, and tape-like samples 80A, 80B, and 80C,respectively, as shown in FIG. 7A, 7B, and 7C. As evident from theabove, it is not limited that the sample may be formed into not only adisk shape but also another shapes.

Assume that the gap length between the distal end of the probe electrode11 and the measurement surface 31a varies during measurement of thesurface potential of the measurement surface 31a due to poor surfaceprecision of the measurement surface 31a or poor rotation precision ofthe sample 31. In such a case, the gap between the vibration center ofthe distal end of the probe electrode 11 and the measurement surface 31ais controlled to be constant by adjusting the variation amount. Such agap control operation will be described below.

A laser beam a1 is emitted from the light source 19 and is incidentthrough the lens system (not shown) and the mirror 21 on the measurementsurface 31a of the sample 31 located right under the distal end of theprobe electrode 11. A reflected laser beam a2 is guided to the PSD 20through the mirror 22. At this time, if the surface precision of themeasurement surface 31a or the rotation precision of the sample 31 ispoor, the sample 31 is displaced vertically, i.e., in the heightdirection. If the sample 31 is displaced vertically, i.e., in the heightdirection, a reflected laser beam a2' of the laser beam a1 incident onthe measurement surface 31a is incident on the PSD 20 while it ishorizontally shifted by an amount as proportional to the displacementamount of the sample 31. An output signal from the PSD 20 is input tothe gap detector 47 and is converted into a voltage having a constantlevel corresponding to the displacement amount of the sample 31. Anoutput signal from the gap detector 47 is compared with a gap settingvoltage, i.e., a reference voltage which is set in the variable voltagepower source 51 of the gap control circuit 48. The difference betweenthe voltages, i.e., a differential voltage is then output to thedifferential amplifier 50. The amplifier 50 amplifies the inputdifferential voltage and applies it to the ga control piezoelectricelement 45. The piezoelectric element 45 expands/contracts in proportionto the applied differential voltage. The arm 43 then vertically pivotson the elastic hinge portion 42a due to the expansion/contraction of thepiezoelectric element 45 and the biasing force of the spring 46. As aresult, the gap between the vibrating center of the probe electrode 11of the vibration type probe 34 attached to the distal end of the arm 43and the measurement surface 31a is controlled to be constant. At thistime, since the distance between the elastic hinge portion 42a and thepiezoelectric element 45 and the distance between the piezoelectricelement 45 and the distal end of the arm 43 are set to be 1:10, thedisplacement amount of the probe electrode 11 of the probe 34 attachedto the distal end of the arm 43 is increased to 10 times theexpansion/contraction amount of the piezoelectric element 45. Hence, thedisplacement amount of the probe electrode 11 becomes large. Forexample, when the expansion/contraction amount of the piezoelectricelement is 20 μm, the displacement amount of the probe electrode 11 hasa dynamic range of 200 μm.

The gap between the vibrating center of the probe electrode 11 and themeasurement surface 31a can be controlled to be constant by driving thedriving motor 53 to rotate the feed screw bar 52 and moving the table 41toward the sample 31. With this control, the surface potential of theentire measurement surface 31a can be easily, accurately, and stablymeasured.

By shielding the surface potential measuring system shown in FIG. 4 fromexternal electric waves, more accurate measurement can be performed.

In the above-described embodiment, the surface potential of thedisk-like sample is measured. However, measurement of a surfacepotential can be performed in the same manner as described above withrespect to a flat, i.e., a card-like, drum-like, tape-like sample oranother shape sample.

FIGS. 9 to 12 show a sample on which measurement experiments areperformed by mean of the surface potential distribution measuring systemshown in FIG. 3, and measurement experiment results. As shown in FIG. 9,radial chromium patterns 31b are deposited on a measurement surface 31aof a disk-like sample 31. The intervals of the chromium patterns 31bvary from the outer periphery to the inner periphery. For example, thechromium patterns 31b are divided into four quadrants A1, A2, A3, and A4at angular intervals of 90°. The quadrant A1 constitutes a 0.3 lines/mm(lp/mm) zone; the quadrant A2, a 2 lp/mm zone; the quadrant A3, a 4lp/mm zone; and the quadrant A4, a 6 lp/mm zone. Note that all thevalues described above are values at the outermost periphery.

As shown in FIG. 10, the sample 31 is fixed on a disk base 31c, and apower source 54 is connected between the chromium patterns 31b and thedisk base 31c. A predetermined voltage is applied to the chromiumpatterns 31b, and the sample 31 and the disk base 31c are rotated. Theprobe electrode is then located near the chromium patterns 31b. Asurface potential on the chromium patterns 31b is measured in the samemanner as in the above-described embodiments.

FIG. 11 shows a experiment result obtained by measuring the surfacepotential of the sample by using the system shown in FIG. 5 withoutoperating the gap control circuit 48 and performing gap control. In thismeasurement experiment, the probe electrode 11 is vibrated at afrequency of 7 kHz. Note that the abscissa and the ordinate in FIG. 11respectively represent time and a measurement output, i.e., an outputvoltage. As shown in FIG. 11, in this system, the influences ofvariations in gap between the probe electrode and the sample aredirectly reflected in the output result, and the small chromium patternsin the quadrants A3 and A4 are not resolved. Hence, it is apparent thatdetection sensitivity in these quadrants is poor. However, relativelyaccurate measurement of surface potentials is performed in otherquadrants A1 and A2. As is apparent from an experiment result to bedescribed later, the surface potential of a sample can be measured withsufficient precision without gap control by increasing the vibrationfrequency of the probe 11.

FIG. 12 shows an experiment result obtained by measuring the surfacepotential of a sample by using the system shown in FIG. 5. In this case,the gap control circuit 48 is operated to perform gap control. In thismeasurement experiment, the probe electrode 11 is vibrated at afrequency of 7 kHz. The sample 31 is rotated once and a voltage of 50 Vis applied to the chromium patterns 31b. The gap between the probeelectrode 11 and the chromium patterns 31b is held at 50±0.8 μm, and thesurface potentials of the outer peripheral portions of the chromiumpatterns 31b are measured. Note that the abscissa and the ordinate inFIG. 12 respectively represent time and a measurement output, i.e., anoutput voltage. As shown in FIG. 12, according to the surface potentialmeasuring system of the present invention, all the chromium patterns inthe quadrants A1, A2, A3, and A4 are stably resolved.

FIGS. 13A, 13B, and 13C respectively show experiment results obtained bymeasuring the surface potential of a sample by using the system shown inFIG. 5. In this case, the gap control circuit 48 is operated to performgap control, and the probe electrode 11 is vibrated at 10 kHz, 1 kHz,and 0 kHz, respectively. In this experiment, similar to the disk-likesample shown in FIG. 9, radial chromium patterns 31b are deposited on ameasurement surface 31a of a sample (not shown). The intervals of thechromium patterns 31b vary from the outer periphery to the innerperiphery. For example, the chromium patterns 31b are divided into fourquadrants B1, B2, B3, and B4 at angular intervals of 90°. The quadrantB1 constitutes a 2 lines/mm (lp/mm) zone; the quadrant B2, a 0.3 lp/mmzone; the quadrant B3, a 5 lp/mm zone; and the quadrant B4, a 3 lp/mmzone. Note that all the values described above are values at theoutermost periphery. As is apparent from FIGS. 13A, 13B, and 13C, as thevibration frequency of the probe electrode 11 is increased, thepotential of the sample can be measured with higher precision. Inaddition, it is found from experimental results that the surfacepotential of the sample can be satisfactorily measured even at avibration frequency of 1 kHz and it is possible that the surfacepotential can be precisely measured at a vibration frequency of 10 kHzwhen the circuit arrangement is so improved as to have a high detectionsensitivity.

It is confirmed, on the basis of the above-described experiment resultsand in consideration of various circuit systems, that the probeelectrode 11 is preferably vibrated at 100 kHz or less, more preferably,between 50 kHz to 100 kHz.

In practice, the system for measuring the surface potential of a sampleaccording to the present invention is applied to a radiation imagingapparatus for forming and observing a fluoroscopic image in a real sizeby using an image plate.

FIG. 14 shows an X-ray imaging apparatus. In this X-ray imagingapparatus, an image plate 52 for forming an X-ray image is housed in acasing 55. A window (not shown) is formed in the bottom of the casing55. An X-ray transmission image is radiated onto the image plate 52through this window.

As shown in FIG. 15, the image plate 52 is formed by stacking a phosphorlayer 66, an ITO layer 67, and a photosensitive layer 68 on an aluminumsubstrate 65. The phosphor layer 66 is constituted by a layer containinggadolinium, iodine, cesium, and the like, e.g., a Gd₂ O₂ SiTb layerhaving a thickness of about 200 μm. The photosensitive layer 68 isconstituted by a layer consisting of an inorganic or organicphotosensitive substance, e.g., an amorphous Si layer having a thicknessof about 20 μm. The gadolinium phosphor layer emits light having a peakat a wavelength of 550 nm upon radiation of X-rays, and hence has a veryhigh luminous efficacy. The amorphous Si photosensitive layer has highsensitivity in a visible region, and has a quantum efficiency of nearly100% with respect to light near 550 nm.

A high-voltage charger 53 for uniformly charging the image plate 52 isarranged in the casing 55. Prior to an imaging operation, the charger 53is scanned/driven on the image plate 52 along a guide (not shown) with asmall gap of about 5 mm ensured with respect to the image plate 52. Withthis operation, the entire surface of the image plate 52 is charged at,e.g., about 500 V.

A dielectric recording sheet 73 on which a latent image formed on theimage plate 52 is transferred and recorded is prepared separately fromthe casing 55. The dielectric recording sheet 73 is formed by bonding adielectric sheet 71 to a frame 72. The dielectric recording sheet 73 isinserted into an insertion port formed in a side portion of the casing55. The sheet 73 is then clamped between a pair of loading/unloadingrollers 53A and 53B and is transferred onto the image plate 52. Atransfer roller 54 is arranged in the casing 55. When the dielectricrecording sheet 73 is transferred onto the image plate 52, the transferroller 54 is scanned/driven along a guide (not shown) while the roller54 urges the sheet 73 against the image plate 52.

An imaging operation will be described in detail with reference to FIGS.16A to 16E which sequentially show an operation of main part of theimaging apparatus in FIG. 15.

FIG. 16A shows a positional relationship between the respective portionsbefore an imaging operation is started. An imaging operation is startedwhen the charger 53 is scanned/driven on the image plate 52 upondepression of a start switch (not shown), as shown in FIG. 16B. Uponapplication of a high voltage of 4 to 7 kV from the charger 53, theimage plate 52 is uniformly charged at about 500 V, as described above.This operation is equivalent to initialization of the image plate 52. Asshown in FIG. 16C, the dielectric recording sheet 73 is then inserted.The sheet 73 is transferred onto the image plate 52, and is caused tooppose the image plate 52 with a gap of about 1 to 2 mm.

Subsequently, an X-ray transmission image is radiated from the substrateside of the image plate 52. If, for example, a human body is to besubjected to fluoroscopic imaging, X-ray radiation is performed at 70keV and about 1 mR. Upon this X-ray radiation, a latent image is formedon the image plate 52. More specifically, the gadolinium phosphor layeremits visible light upon X-ray radiation, and the charges on theamorphous Si layer corresponding to the portions from which the light isemitted are discharged to the grounded substrate in accordance with thelight emission amounts of the respective portions. As a result, apotential pattern of 500 to 50 V is formed in accordance with thetransmission image.

Subsequently, as shown in FIG. 16D, the transfer roller 54 isscanned/driven along the guide, and a dielectric sheet 71 of thedielectric recording sheet 73 is urged against the image plate 52. Withthis operation, the latent image on the image plate 52 is transferredonto the dielectric sheet 71. In this transfer process, a referencevoltage is applied from an electrode (not shown) to the dielectricexhausted recording sheet 71. As described above, similar to a potentialapplied to the correcting electrode 70, this reference voltage is usedfor correction of a voltage from the surface potential measuring circuit40 shown in FIG. 4. The dielectric recording sheet 73 on which thelatent image is transferred and recorded is exhausted outside the casingby the rollers 53A and 53B, as shown in FIG. 16E. Thereafter, a newdielectric recording sheet is set, and the flow of processing returns tothe step in FIG. 16A.

The latent image formed on the recording sheet 73 in this manner is readby a surface potential measuring system shown in FIG. 17 havingsubstantially the same arrangement as that of the system shown in FIG.4.

The surface potential measuring system shown in FIG. 17 is differentfrom the one shown in FIG. 4 in that X- and Y-axis tables 81 and 82 arearranged on a stage 30 so as to be driven by X- and Y-axis drivingmotors 83 and 84, respectively. The dielectric recording sheet 73 onwhich the latent image is formed is placed on the Y-axis table 82. Fromthe sheet 73, the potential image is sequentially picked up by a probeelectrode 11 which is slightly vibrated by a vibrating piezoelectricelement, and is extracted, as an image signal, by a surface potentialdetector 40.

The vibrating piezoelectric element is attached to the distal end of anarm 43 of a gap control mechanism mounted on the X-axis table 81. Thegap control mechanism includes a gap adjusting screw 44, a balancingspring 46, and a gap control mechanism driving piezoelectric element 45.This piezoelectric element is controlled by a gap control circuit 48 sothat optimal control of the gap between the vibrating center of theprobe electrode 11 attached to the distal end of the arm 43 and therecording sheet 73 is automatically performed.

For this gap control, a gap position detecting optical system and a gapdetector 47 are coaxially arranged at a position where the probeelectrode 11 is attached. With this arrangement, a light beam isradiated from the optical system onto the recording sheet 73. Upondetection of the light beam reflected by the sheet 73, the gap detector47 detects a gap. The detected gap is then fed back to the piezoelectricelement 45 through the gap control circuit 48.

In such a surface potential measuring system, while the probe electrode11 is slightly vibrated, the gap between the vibrating center of theprobe electrode 11 and the recording sheet 73 is accurately andautomatically controlled, and the latent image on the recording sheet 73is read by X-Y scanning.

As described above, according to the present invention, when a real-sizeX-ray transmission image is to be imaged, as a latent image, on aphotosensitive layer and to be read, the latent image is firsttransferred and recorded on a dielectric recording image by urging thephotosensitive layer against the recording sheet. With this operation,the image can be read without attenuation in the image potential, andhence a uniform reproduced image can be obtained.

In addition to the above-described X-Y scanning, the latent image on thedielectric recording sheet 73 can be read by the rotating disk typesystem shown in FIG. 4. In this case, a dielectric recording sheethaving a rectangular frame must be transferred onto a disk.

FIG. 18 shows a method for such an operation. In this method, thedielectric sheet 71 of the dielectric recording sheet 73 is cut by acutting jig 91 and a press piston 92, and i simultaneously bonded to adisk 93. The cutting jig 91 has a cylindrical shape and a blade formedon its distal end. The press piston 92 is coaxially fitted in thecutting jig 91. The disk 93 has an outer diameter allowing it to befitted in the jig 91. An adhesive agent is coated on the lower surfaceof the disk 93 in advance. While the disk 93 is fitted in the distal endof the cutting jig 91, the jig 91 is brought into contact with thedielectric sheet 71 on which a latent image is formed. By operating thepress piston 92 and the cutting jig 91, the disk 93 is bonded to thesheet 71, and at the same time, the sheet 71 is cut off. With thisprocess, a rotating disk on which the dielectric sheet 71 is bonded canbe obtained. The image on the rotation disk is read by the system shownin FIG. 4.

The present invention is not limited to the above-described embodiment.In the embodiment, an X-ray transmission image is radiated from thesubstrate side of the image plate. However, since X-rays are transmittedexcept for the phosphor layer, an X-ray transmission image may beradiated from the upper surface side of the image plate.

According to the system shown in FIG. 17, when a real-size X-raytransmission image is to be formed by using an image plate, an excellentreproduced image can be obtained by preventing attenuation in the imagepotential of the photosensitive layer.

As has been described above, in the vibration type probe structure ofthe present invention, the distal end of the probe electrode is locatednear a measurement surface, and the surface potential of the measurementsurface is measured by vibrating the probe electrode in a directionperpendicular to the measurement surface. With this arrangement,excellent detection sensitivity and high measurement resolution can berealized, thus enabling high-precision measurement in a small area.

In addition, according to the present invention, a reference voltage isapplied to the correcting electrode formed on a portion of a measurementsurface. A detection signal output from the surface potential measuringsystem at this time is input to the arithmetic means. With thisoperation, a measurement error of the surface potential of themeasurement surface due to drift such as temperature drift can becorrected on the basis of the input detection signal. Therefore, ahigh-precision measurement value can be stably obtained.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices, shownand described herein. Accordingly, various modifications may by withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A system for measuring a surface potential of asample, comprising:probe means, having a distal end located near ameasurement surface of the sample with a gap therebetween and having avibrating center, for probing the surface potential; vibrating means forvibrating said probe means with respect to the vibrating center tochange the gap between the distal end and the measurement surface;detecting means for detecting a change in potential of the distal end ofsaid probe means and converting the change into a measurement signalcorresponding to the surface potential of the sample; and means forcontrolling said vibrating means to maintain a constant distance betweenthe vibrating center and the measurement surface.
 2. A system accordingto claim 1, wherein said vibrating means vibrates the distal end of saidprobe means at a predetermined frequency not smaller than 1 kHz.
 3. Asystem according to claim 1, wherein said vibrating means includes meansfor generating an oscillation signal having a predetermined frequencynot smaller than 1 kHz and elongation and contraction means beingelongated or contracted in response to the oscillation signal so as tovibrate said probe means.
 4. A system according to claim 3, wherein saiddetecting means includes means for converting a potential of the distalend of said probe means into a potential signal, and detection means fordetecting the potential signal with the oscillation signal andgenerating a measurement signal.
 5. A system according to claim 4,wherein said detecting means further includes integrating means forintegrating and averaging the measurement signal to generate an averagedmeasurement signal.
 6. A system according to claim 1, further comprisingmeans for displaying the measurement signal.
 7. A system according toclaim 1, wherein said vibrating means includes a piezoelectric element.8. A system according to claim 1, wherein said probe means includes aprobe electrode and means for supporting said probe electrode.
 9. Asystem according to claim 8, wherein said supporting means includes acylindrical housing in which said probe electrode is fixed, the distalend of said probe electrode being projected from said cylindricalhousing.
 10. A system according to claim 9, wherein said supportingmeans further includes an insulating member received in the cylindricalhousing, said probe electrode being fixed by the insulating member inthe cylindrical housing.
 11. A system according to claim 9, furthercomprising:means for shielding said probe means, said vibrating meansand said detecting means from an electro-magnetic wave.
 12. A systemaccording to claim 1, wherein said controlling means includes means fordetecting a distance between the vibrating center and the measuringsurface to generate a gap signal.
 13. A system according to claim 12,wherein said controlling means includes means for moving said probemeans which vibrates in response to the gap signal.
 14. A systemaccording to claim 1, further comprising means for moving the samplealong the measurement surface.
 15. A system according to claim 1,further comprising means for rotating the sample.
 16. A system accordingto claim 1, further comprising reference means having a referencepotential to be detected by said probe means.
 17. A system according toclaim 16, further comprising correcting means for correcting ameasurement signal corresponding to the surface potential of the sampleby using a measurement signal corresponding to the reference potentialof said reference means which is converted by said detecting means. 18.A system according to claim 17, wherein said correcting means includesmeans for generating a correction signal by processing the measurementsignal corresponding to the reference potential, and means for storingthe correction signal.
 19. A system according to claim 1, furthercomprising said probe means including a needle-like electrode having thedistal end.
 20. A system for measuring a surface potential of a sample,comprising:probe means, having a distal end located near a measurementsurface of the sample with a gap, for probing the surface potential;vibrating means for vibrating said probe means to change the gap betweenthe distal end and the measurement surface; and detecting means fordetecting a change in potential of the distal end of said probe meansand converting the change into a measurement signal corresponding to thesurface potential of the sample; wherein said controlling means includesmeans for detecting a change of a gap between the surface of the sampleand a given reference surface and generating a gap signal; and whereinsaid means for generating the gap signal includes means for generating alight beam and directing the light beam to the measurement surface, andmeans for detecting the light beam reflected by the measurement surface,and detecting a displacement of the reflected beam which is dependent ona change of the sample with respect to the reference surface, therebygenerating the gap signal.
 21. A system for measuring a surfacepotential of a sample having a surface region, comprising:probe means,having a distal end located near a measurement surface of the samplewith a gap and having a vibrating center, for probing the surfacepotential of the measurement surface; vibrating means for vibrating saidprobe means with respect to the vibrating center to change the gapbetween the distal end and the measurement surface; holding means forholding said problem means so as to allow said probe means to bevibrated; means for controlling the holding means to maintain a constantdistance between the vibrating center and the measurement surface; anddetecting means for detecting a change in potential of the vibrateddistal end of said probe means and converting the change into ameasurement signal corresponding to the surface potential of the sample.22. A system according to claim 21, wherein said vibrating meansvibrates the distal end of said probe means at a predetermined frequencynot smaller than 1 kHz.
 23. A system according to claim 21, wherein saidvibrating means includes means for generating an oscillation signalhaving a predetermined frequency not smaller than 1 kHz and elongationand contraction means being elongated or contracted in response to theoscillation signal so as to vibrate said probe means.
 24. A systemaccording to claim 23, wherein said detecting means includes mans forconverting a potential of the distal end of said probe means into apotential signal, and detection means for detecting the potential signalwith the oscillation signal and generating a measurement signal.
 25. Asystem according to claim 24, wherein said detecting means furtherincludes integrating means for integrating and averaging the measurementsignal to generate an averaged measurement signal.
 26. A systemaccording to claim 21, further comprising means for displaying themeasurement signal.
 27. A system according to claim 21, wherein saidvibrating means includes a piezoelectric element arranged between saidholding means and said probe electrode.
 28. A system according to claim21, wherein said holding means includes a cylindrical housing in whichsaid probe means is fixed, the distal end of said probe means beingprojected from said cylindrical housing.
 29. A system according to claim28, wherein said holding means further includes an insulating memberreceived in the cylindrical housing, said probe means being fixed by theinsulating member in the cylindrical housing.
 30. A system according toclaim 21, wherein said maintaining means includes means for detecting achange in height of the measurement surface with respect to a givenreference surface and generating a height signal.
 31. A system accordingto claim 30, wherein said maintaining means includes means for movingsaid holding means in response to the height signal.
 32. A system formeasuring a surface potential of a sample having a surface region,comprising:probe means, having a distal end located near a measurementsurface with a gap therebetween, for probing the surface potential ofthe measurement surface; vibrating means for vibrating said probe meansto change the gap between the distal end of said probe means and themeasurement surface; holding means for holding said probe means which isvibrated by said vibrating means, so as to allow said probe means to bevibrated; means for maintaining a substantially constant gap betweensaid holding means and a region detected by said probe means; anddetecting means for detecting a change in potential of the vibrateddistal end of said probe means and converting the change into ameasurement signal corresponding to the surface potential; wherein saidmaintaining means includes means for detecting a change in height of themeasurement surface with respect to a given reference surface andgenerating a height signal; and wherein said means for generating theheight signal includes means for generating a light beam and directingthe light beam to the measurement surface, and means for detecting thelight beam reflected by the measurement surface, detecting adisplacement of the reflected light beam which is dependent on a changein height of the measurement surface with respect to the referencesurface, and generating a height signal.
 33. A system according to claim21, further comprising means for moving the sample along the measurementsurface.
 34. A system according to claim 21, further comprising meansfor rotating the sample.
 35. A system according to claim 21, furthercomprising reference means having a reference potential to be detectedby said probe means.
 36. A system according to claim 35, furthercomprising correcting means for correcting a measurement signalcorresponding to a surface potential of the sample by using ameasurement signal corresponding to the reference potential of saidreference means which is converted by said detecting means.
 37. A systemaccording to claim 36, wherein said correcting means includes means forgenerating a correcting signal by processing the measurement signalcorresponding to the reference potential, and means for storing thecorrecting signal.
 38. A system according to claim 21, furthercomprising:means for shielding said probe means, vibrating means anddetecting means from an electro-magnetic wave.
 39. A system according toclaim 21, further comprising said probe means including a needle-likeelectrode having the distal end.
 40. A system for measuring a surfacepotential of a sample, comprising:a needle electrode which has a distalend located near a measurement surface of the sample with a gaptherebetween, for probing the surface potential; vibrating means forvibrating said needle electrode to change the gap between the distal endand the measurement surface; detecting means for detecting a change inpotential of the distal end of said probe means and converting thechange into a measurement signal corresponding to the surface potentialof the sample; and means for controlling said vibrating means tomaintain a constant distance between the vibrating center and themeasuring surface; wherein said needle electrode has a vibrating centerand said vibrating means vibrates said needle electrode with respect tothe vibrating center.
 41. A system for measuring a surface potential ofa sample comprising:a needle electrode which has a distal end locatednear a measurement surface of the sample with a gap therebetween, forprobing the surface potential; vibrating means for vibrating said needleelectrode to change the gap between the distal end and the measurementsurface; detecting means for detecting a change in potential of thedistal end of said probe means and converting the change into ameasurement signal corresponding to the surface potential of the sample;and controlling means for controlling a gap length between the distalend of said electrode and the measurement surface within a predeterminedrange.
 42. A system according to claim 41, wherein said needle electrodeis vibrated at a vibration frequency not smaller than 1 kHz.
 43. Asystem according to claim 41, wherein said vibrating means includesmeans for generating an oscillation signal having a predeterminedfrequency not smaller than 1 kHz and elongation and contraction meansbeing elongated or contracted in response to the oscillation signal soas to vibrate said probe means.
 44. A system according to claim 41,wherein said detecting means includes means for converting a potentialof the distal end of said probe means into a potential signal, anddetection means for detecting the potential signal with the oscillationsignal and generating a measurement signal.
 45. A system according toclaim 44, wherein said detecting means further includes integratingmeans for integrating and averaging the measurement signal to generatean averaged measurement signal.
 46. A system according to claim 41,further comprising means for displaying the measurement signal.
 47. Asystem according to claim 41, further comprising means for supportingsaid electrode.
 48. A system according to claim 41, wherein saidvibrating means includes a piezoelectric element.
 49. A system accordingto claim 47, wherein said supporting means includes a cylindricalhousing in which said electrode is fixed, the distal end of saidelectrode being projected from said cylindrical housing.
 50. A systemaccording to claim 49, wherein said supporting means further includes aninsulating member received in the cylindrical housing, said electrodebeing fixed by the insulating member in the cylindrical housing.
 51. Asystem according to claim 41, wherein said controlling means includesmeans for detecting a change of a gap between the surface of the sampleand a given reference surface and generating a gap signal.
 52. A systemaccording to claim 51, wherein said controlling means includes means formoving said electrode which vibrates in response to the gap signal. 53.A system according to claim 51, wherein said means for generating thegap signal includes means for generating a light beam and directing thelight beam to the measurement surface, and means for detecting the lightbeam reflected by the measurement surface, and detecting a displacementof the reflected beam which is dependent on a change of the sample withrespect to the reference surface, thereby generating the gap signal. 54.A system according to claim 41, further comprising means for moving thesample along the measurement surface.
 55. A system according to claim41, further comprising means for rotating the sample.
 56. A systemaccording to claim 41, further comprising reference means having areference potential to be detected by said electrode.